This invention relates to a method for extending the range of operation of an electromagnetic fuel injector.
An electromagnetic fuel injector is a device which has an inductive element associated with it. The inductive element causes the pintle of a valve within the electromagnetic injector to open upon energization of the inductive element. When this occurs, the pintle moves to a position that allows pressurized fuel to be discharged from the injector into the intake conduit leading to the combustion chamber of an internal combustion engine. The injector may be centrally located so that it alone or in combination with another injector supplies all of the fuel required for combustion or, alternatively, may be used to supply fuel to only one of the engine's combustion chambers.
A problem of the prior art has been the accurate determination of the quantity of fuel that is delivered from a fuel injector operated intermittently. Intermittent fuel injection operation is desirable because it permits a fuel injection system to control the fuel delivery rate by variation of the width of an electrical voltage pulse applied to the inductive element of the electromagnetic injector. Also, intermittent operation allows a higher fuel delivery rate during the pulse duration so that a lesser degree of precision in injector manufacture is required and so that the point at which the fuel is delivered to a particular combustion chamber can be controlled.
If the range of operation of an electromagnetic fuel injector is sufficiently great to permit engine operation at maximum engine speed and loads, then the fuel delivery rate at low engine speeds and loads may be unpredictable. The reason for this is that the inductive characteristics of the inductive element in the electromagnetic fuel injector produce variation in the response time of the device as a function of the applied voltage and the individual injector properties. The electromagnetic injectors are energized for times of a few milliseconds and the length of time of the pintle movement at low fuel injector pulse widths is critical to accurate fuel metering. To assure that there is sufficient fuel to produce combustion, it is necessary at low engine speeds and loads to provide an excess of fuel. This assures that enough fuel for combustion is present and that engine misfires do not occur. Necessarily, the excess fuel supply reduces fuel economy and can increase hydrocarbon exhaust emissions.